Spool valve assembly



July 20, 1965 H. J. STACEY SPOOL VALVE ASSEMBLY 2 Sheets-Sheet 1Original Filed May 12, 1959 m m m m i J l n m 5 2;; 7. n1 r O l l 2 a 7F I. W YB E 4 m m & & H M A u w m a a 1 9 a 5 2 7 1 1 9 ,7 e fl 2 l o ll5 5 w a 5 5 5/ 5 2 A M 6 5 H, mm M- i w 4 w 9 55% 3 9 r a w 5 .5 2 a a AJ 2 Y 1. 7 6 A 3 7 r 3 3 3 7 2 i M i INVENTOR.

HUGH J. STACEY TORNEYS y 0, 1965 H. J. STACEY 3,195,559

SPOOL VALVE ASSEMBLY Original Filed May 12, 1959 2 Sheets-Sheet 2INVENTOR. HUGH J. STACEY BY 9%, 77/0,? 9 19M ATTORNEYS United StatesPatent 3,195,559 819681, VALVE ASSEMBLY Hugh J. Stacey, Chesterland,Ghio, assignor to Parker- Hannifin Corporation, @ieveiand, Ghio, acorporation of Ohio Continuation of application Ser. No. 812,687, May12, 1959. This application Dec. '7, 1962, Ser. No. 243,714

13 Claims. (Cl. 137-27ii) Lower positions in which the pressure inletport is selectively communicated with one of the service ports to eitherraise or lower the bucket, blade, or other implement to which the pistonin the cylinder assembly is operatively connected, and in which theother service port is communicated with the tank port; and a Floatposition in which the pressure inlet port is communicated with eachother to permit descent of the implement, and thus of the piston in thecylinder, by gravity.

In a broad sense, spool valves of this type are known in the art, itbeing one principal aim of the present invention to provide a novelrestriction arrangement between one service port and the tank port whichis effective to build up back pressure in the return circuit so thatcavitation in the pressure circuit is prevented, as when the spool is inLower position. Thus, when the bucket or blade engages the ground fullline pressure will be immediately available for penetration or diggingaction.

It is another object of this invention to provide a spool valve assemblyof the character indicated in which the valve spool is hollow and isprovided with a novel restriction therein which, in the Float positionof the spool, communicates the head end of the cylinder with the tankport to accommodate the greater displacement as compared with that ofthe rod end, such restriction also being effective to build up backpressure during the float or down stroke of the piston under theinfluence of the load thereon (the bucket or blade and its supportingarm) so that the rod end of the cylinder will be kept filled with oilpreparatory to power lowering at a greater speed.

It is another object of this invention to provide a spool valve assemblyof the character indicated in which the spool assembly may be turned endfor end in the valve housing so that its actuating portion is disposedat either end of the valve housing.

It is yet another object of this invention to provide a spool valveassembly of the character indicated in which the relief valve in thevalve housing may, likewise, be turned end for end so as to place theadjusting mechanism therefor at either end of the valve housing.

It is still another object of this invention to provide a novel sleeveextension arrangement which extends part way into the passage leading tothe tank port to serve as a cut-off for fluid flow through the hollowspool when the latter is shifted to Raise position, whereby pressurebuilds up in the hoist cylinder to effectively raise the implementactuated by the piston therein.

Other objects and advantages of the present invention will becomeapparent as the following description proclaims, the followingdescription and the annexed drawing setting forth in detail a certainillustrative embodiment of the invention, this being indicative,however, of but one of the various ways in which the principle of theinvention may be employed.

In said annexed drawing:

FIG. 1 is a cross-section view through the valve assembly in a planecontaining the axes of the relief valve and of the valve spool;

FIG. 2 is a fragmentary cross-section view taken substantially along theline 22, FIG. 1; and

FIG. 3 is a cross-section view taken substantially along the line 33,FIG. 1.

Referring now more particularly to the drawing, the valve assembly 1herein shown comprises a valve housing 2 formed with mounting holes bywhich it may be secured in place and further formed with a pressureinlet port 4 which intersects the relief valve bore 5, the check valvebore 6, and the valve spool bore 7, the latter at two places 8 and 9.The housing 2 is formed with a tank port 10 which has a top branch 11and a bottom branch 12 intersecting relief valve bore 5 and spool bore 7as shown and a middle branch 14 which intersects only spool bore 7.

The housing 2 is additionally formed with two service or cylinder ports15 and 16 which intersect the spool bore '7 at regions adjacent therespective tank port branches 11 and 12, and as indicated by the lines17 and 18, one service port 15 is connected to the head end of a doubleacting cylinder assembly 19 and the other service port 16 is connectedto the rod end of said double acting cylinder assembly 19.

The check valve bore 6 has a pair of spring-biased check valves 20therein. The inlet side of each check valve 26 communicates by way ofbore 6 with the pres sure inlet port 4 and when the check valves areunseated, fluid flows therepast into the respective secondary inletports 21 and 23, one of which is disposed between the top service port15 and the top branch 8 of the inlet port 4 and the other of which isdisposed between the bottom service port 16 and the bottom inlet branch9.

With reference to the relief valve bore 5 which is intersected by thetank port branches 11 and 12, there is disposed in one portion of suchbore a threaded plug 25 which serves as an abutment for the tubularrelief valve seat member 26, the plug being sealed as by means of theO-ring 27, and the tubular end of the seat member being sealed in bore 5as by means of an O-ring 28.

Screwed into the other and identical end of the relief valve bore 5 is arelief valve bonnet 29 which serves to retain the valve guide sleeve 30in place with its inner end coaxial with, but axially spaced from, theseat 31. Slidably guided in said sleeve 30 is the tubular relief valvemember 32 which is pressed by the spring 34 to cause its lower end toengage seat 31 in fluid-tight manner, the reilef valve member 32 beingsealed in the sleeve 30 as by means of the O-ring 35. The upper end ofthe spring 34 bears on the spring guide 36 which, in turn, is engaged byan adjusting screw 37 which has threaded engagement in the bonnet 29 andwhich is locked in adjusted position by means of the lock nut 38 and cap39, there being intervening washers it? between the bonnet and lock nutand between the lock nut and the cap respectively.

As is evident, whenever the pressure in the inlet port 4 acting on theannular area A is less than the force exerted by the spring 34, therelief valve member 32 will remain in seated position. However, shouldthe fluid pressure in port 4 increase to an extent such that the forceon the annular area A exceeds the force exerted by the spring 34-, therelief valve member 32 will be forced upwardly away from the seat 31,whereupon, fluid may flow through Patented July 20, 1965,

the tubular seat member '2 into the bottom branch 12 of the tank port10. a

It is to be noted that the relief valvebore is-the same at both ends sothat the entirerelief valve assembly may be reversed end for end tobring the adjusting mechanism to the bottom portion of the bore, asviewed in FIG. 1. I

Thus, in the event of encountering close quarters at: the r top of thevalve housing 2'with insuificient room for removal of the cap 39 .andturningof the adjusting screw .37 aswith a screwdriver or the like, therelief valve assembly may be reversed to'place the screw 37at thebottom. V

Referring now in detail to the. valve spool 45 andits cap 39 andadjusting spring-centering and float-position detent mechanism, it

can be seen that the'spool 45 is of' hollow-construction with one end ofthe hole 46 closedby a plug 47 which is threadedly engaged therewithandwhich is formed with a crossbore 48 for an actuator (not shown).

45 is a close sliding fit inthe spool'bore 7.

Starting at. the actuating end of the. spool: there are providedalternatelands and grooves with the lands 50,

The spool 51, 52, 53, and 54, separ'ated'by intervening .gro'ovesSd, V

57, 58, and 5?, respectively. The lands 5t), 51., 53, and 54, are each,formed with metering slots, as shown, and,

in addition, thelands 50, and 53, are formed with open-' ings or slots60 and ,61 which intersect the spool hole id for reasons whichiwill bepresently explained' Finally, the land 51 just beneath the meteringslotjthereof is formed with. an'orifice 62, the purpose for'whichlikewise will be explained in detail. p

Here again, as in connection with the relief valve bore 5, the spoolbore 7 "issymmetrical withrespect tothe centerline'of the inlet and tankports 4 and 10, such bore and within the part 1%, by means of internaland external 'O-rings as shown and, if desired, a wiping type seal 197may be provided between parts 164 and 10510 wipe foreignmattter fromthesurface of the spool '45. as the spool is moved down or up to'itsseveral different positions. The packing assembly may be held in placeas by screws ldrwthat, extend. through parts 103 and 105 and I t thathave threaded engagement with housing 2.

From the foregoing description it is clear that by reason of thesymmetrical formation of thespool bore 7 with its enlargements 53 andcounterbores 64, the sleeve 100 and associated packing assembly and therestrictor sleeve 70 and associated spring-centering assembly, may bereversed end for end "with the packing assembly at the top and thespring-centering assembly at the bottom, as viewed in FIG. 1. Of course,when such sleeves and their associated assemblies are reversed, thevalve spool 45 must also be and 50-51, which prevent flow of fluidbetween the respec- 7 being formed with an enlargement 63 andcounterbore 64 at each end. p a t Fitted in the enlargement 63 in oneend of the spool bore 7 is a restrictor'sleeve 70 which, adjacent itsiower end, is formed with one or more restricted passages 71 tiveservice ports and 6 and the top and bottom branches 11 andlz of the tankport 10 and which prevent flow of fluid between the service ports andthe re spective secondary inlet branches 21 and 23.

Now, in order to raisethe piston 115 in the cylinder 116 and thus liftor hoist the load, such as a bucket and arm, or a blade and" arm, etc.,the spool 45 is moved to the raise positio'nFR, whereby fluid underpressure in the inlet port 4- unseats the'upper check valve socommunicating the annular space 72 therewithin with the 7 spool valvebore enlargement 63 by means of internal and 7 external O-rings 73 and74. The restrictor sleeve 'is held in place as by means of a plate 75which is seated in the counterbore 64. I

The upper end of the spool 45 has engaged with a shoulder thereof aspring retainer and axially spaced therefrom is another spring retainer81' which engages a snap ring 82 fitted into. a groove in'the spool, thespring 83 being compressed between said retainers 8i) and 81. The upperend of the spool is formedwith a head 84 which is engaged inacounterbore in the detent member 85 which, adjacent its lower end, isformed with a pcripheral groove 86 and which, adjacent its upper'end, isformed -with a beveled shoulder 87, the split resilient that fluid flowsinto the upper secondary inlet 21, through the groove 59 of'th'e spool45', through thefservice port 15 and line 17, into the head end of thecylinder 116. The fluid displaced from the rod end of the cylinder 116flows through the line 18 to the other service port 15, through thegroove. 56,,an-d through the bottom branch 1215f the tank port 10 viathe space between the end of lower sleeve 1th) and surface 101. It is tobe noted that as the spool is, shifted from N to R, the slots 60 areprogressively restricted by sleeve while the orifice 62 is progressivleycommunicated with the bottom secondaryinlet 23,. and, .thereafter themetering slots of land 53 gradually cut off the flow from top inletbranch 8' to middle-tank branch 14 so that pressure builds up in serviceport 15 for hoisting of the load on piston 115.

' As the spool 45 is so moved to R position the top spring ring 89 orthe like, being normallyengaged with the beveled shoulder 87 wherebyspring 83 'maintains the spool 45 in fNeutral position, as shown inFIG. 1. The split resilient ring 89 is contained'in a groove formedbetween the parts 90, and 91 which are threaded together and sealed asby means of the O-ring 92. The functions of the spring-centering anddetent mechanism will pres ently be described in connection with thefour different positions to which'the spool 45 may be shifted. The,

retainer 81is moved downwardly therewith to further compress the spring83, whereby whenvspool actuating force isreleased, the expansive forceof the spring 83 will automaticallyreturn the spool 45 to neutralposition Now, let us assume that it is desired to lower thepiston 115and load underpower control at a rapid rate. To do this, the spool 45is. moved to lower position L,

whereby the bottom spring retainer 80 moves upwardly with the spool tofurthercompr ess the spring 83 against the top retainer 81, the :detentmember tls being held in place by the spring ring 89 which engages thebeveled shoulder 37. During the initial portion of the movement i ofthespool from neutral position N to lower position L, the slots 66 areprogressively-cutoff,- the metering slots in land 51 come into play togradually out Oh? the a shoulder or flange 192 which is disposed inclampedposition in a groove defined .by the parts 103,104, and,

of. a packing assembly, the part 103 being'seated in the counterbore andsealed by means of the O-ring 106,

and the intermediate part being sealed to thespool land bottom inletbranch 9 from the, middle tank branch 14, and the spool orifice 62issb'roughtinto communication with the bottom inlet branch 9. In thelower position LTof the spo0l-45 fluid under, pressure flows from theinlet port 4 through the, bottom check valve 24) into thesecondary inlet23 and past the groove 56 of the spool into the service port 16, andthence through the line 18 to the rod end of the cylinder 116, therebyaiding gravity in moving the piston 115 and load downwardly. The fluiddisplaced from the head end of the cylinder 116 flows through the line1'7 into the service port 15 and thence past the groove 59 of the spoolinto the top branch 11 of the tank port by way of the restrictedpassages 71 in the restrictor sleeve 7d and thus, a back pressure willbuild up in the head end of the cylinder 115 to prevent cavitation inthe rod end and to keep the rod end filled with fluid. The slots 61) andorifice 62 are at this time respectively in communication with thebottom service port 16 and with the bottom branch 9 of the inlet port 4.When the spool actuating force is released, the spring 83 acting on thebottom retainer 8t) and spool will automatically return the spool fromlower position 1" to neutral position N.

When it is desired to connect together the head and rod ends of thecylinder 116 which is at the so-called float position, the spool 45 ismoved up all the way to the float position F, whereby the detent member85 will be shoved up and the beveled shoulder 87 thereof will expand thespring detent ring 89. The expansive force of the spring 83 will nowmove the detent member 85 with respect to the spool 45 until the detent39 springs into the groove 86 thereof. In such float position F, the topbranch 8 of the inlet port 4 is communicated with the center branch 14of the tank port 10 by way of the spool groove 57. In this positionalso, the service ports 15 and 16 are communicated with each otherthrough the slots 61 and 69 and the spool hole 46. Thus, as the piston115 with its load floats downwardly by gravity, the fluid displaced fromthe head end of the cylinder 116 flows through line 17 into the serviceport 15 and through the slots 61 and spool hole 46 to the slots 60 andthrough the slots 61 and spool hole 46 to the slots 60 and other serviceport 16 and thence by way of the line 13 into the rod end of thecylinder 116. Because the displacement of the head end is greater thanthat of the rod end, the excess fluid will be returned to the tank byway of the spool orifice 62 which now is in communication with thecenter branch 14 of the tank port 19. The orifice 62 is of such sizethat a slight back pressure is built up to prevent too rapid descent ofthe piston 116 and its load, whereby the rod end of the cylinder willalways remain filled with fluid ready for immediate power lowering byshifting the spool 45 I from the float position F, to the lower positionL.

It will be seen that the spring detent 89 engaged in the groove 86 willretain the spool 45 in the float position'F until it is manually shifteddownwardly to disengage the detent 89 from the groove 86, whereupon thehead 84 will move the detent member 85 to set the detent ring 89 againstbeveled shoulder 87, the latter action occurring when the spool hasmoved downwardly to the neutral position. Such float position allows thepiston 115 to move in the cylinder 11d and it may be desired to followup by power lowering to effect penetration or digging action of thebucket or blade.

As aforesaid, the formation of the valvespool bore 7 in symmetricalfashion from its middle to its opposite ends enables mounting of therestrictor sleeve 71) and centering spring and detent mechanism ateither end thereof with the sleeve 1% and packing assembly at the otherend.

With further reference to the sleeve 11th as shown in FIG. 1, it is tobe noted that it extends into the tank port branch 12 and terminatesshort of the surface 191, whereby when the valve spool 45 is shiftedfrom position N for free flow of fluid as aforesaid. Moreover, when therelief valve member 32 is forced away from the seat 31 the relievedfluid will flow from the inlet port 4 into the tank port branch 12 andwill freely flow around the annular space between the sleeve ltltl andthe tank port branch 12 to the tank port 10.

The sleeve 1% extending into the tank port branch 12, as shown in FIG.1, affords prompt cutoff of the slots 6%) from the bottom tank portbranch 12 when the spool 45 is shifted from position N to position Rand, similarly, the slots 6i) are rather promptly communicated with theservice port 16 as the spool 45 is shifted, for example, from position Nto position F. Accordingly, the sleeve 1% makes possible the use ofshorter strokes of the spool 45 thereby minimizing the length of thehousing 2 in a direction axially of the spool bore 7. The sleeve 1% alsomakes possible the use of a housing 2 of minimum thickness since thetank port branches 11 and 12 are of substantial axial extent, wherebythey need be of smaller diameter than otherwise to afford free flow offluid as aforesaid through the annular space defined be tween the sleeve1431) and the surrounding tank port branch 11 or 12, as the case may be.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims, or the equivalent ofsuch, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. A spool valve assembly comprising a housing formed with a boreintersected axially therealong by a pressure inlet port, a tank port,and a pair of service ports adapted for connection with a hydrauliccylinder assembly to raise and lower a load on the piston thereof; ahollow valve spool axially reciprocable in such bore and formed withalternate lands and grooves and with openings through certain landsthereof to provide a neutral positon whereat said inlet and tank portsare in fluid communication and said service ports are blocked by landsof said spool, two operating positions whereat said inlet and tank portsare communicated selectively with said service ports to actuate suchcylinder assembly in either di rection; and a float position whereatsaid service ports are communicated with each other and said inlet andtank ports are communicated with each other; and restrictor meanseffective, in one operating position only, to build up a back pressurein one service port when that service port is communicated with saidtank port; said restrictor means comprising a perforate sleeve mountedin said housing to constitute an extension of such bore and throughwhich fluid flows from said one service port to said tank port.

2. A spool valve assembly comprising a housing formed with a boreintersected axially therealong by a pressure inlet port, a tank port,and a pair of service ports adapted for connection with a hydrauliccylinder assembly to raise and lower a load on the piston thereof; ahollow valve spool axially reciprocable in such bore and formed withalternate lands and grooves and with openings through certain landsthereof to provide a neutral position whereat said inlet and tank portsare in fluid communication and said service ports are blocked by landsof said spool, two operating positions whereat said inlet and tank portsare communicated selectively with said service ports to actuate saidcylinder assembly in either direction, and a float position whereat saidservice ports are communicated with each other and said inlet and tankports are communicated with each other; said service ports, in the floatposition of said spool, being communicated with each other through theinterior of said spool, and said spool being formed with an orificewhich leads from the interior thereof to said tank port whereby, in thecase of a differential displacement cylinder assembly, excess fluid fromI one end flows through such orifice to the tank port andv back pressurebuilds up in the interior of said spool to prevent cavitation in theother end of such cylinder assembly, such orifice and one of theopenings in said spool being arranged so that in one operating positionof said spool they communicate'the inlet portwith the same service portthat is at that time communicated with said inlet port, and a sleeve insaid housing extending into said tank;

port and constituting an extension of such 'hore efiectiveto block suchopening as said spool is moved from neutral position to the otheroperating position.

3. A spool valve assembly comprising a housing formed j with aboreintersected axially therealong by a pressure inlet port, a tank port,and a pair of service ports adapted for connection with a hydrauliccylinder assembly to raise; and lower a load on the piston'thereof;a'hollow valve spool axially reciprocable in such bore and formed withalternate lands and grooves and with openings through certain landsthereof to provide a neutral position whereat said inlet and tank portsare in fluid communication and said service ports are blocked by landsof said spoolftwo operating positions whereat said inlet and tankportsare alternatelands and grooves to. provide a neutral positionwhereatsaid inlet and tank ports are in fluid communication and saidservice ports are blocked by lands 'ofsa id spool, and two operatingpositions wherea-t said inlet and tank ports are communicatedselectively with said service ports to'actuate such cylinder assembly ineither direction; a pair of longitudinally spaced openings in said valve[spool in fluid communication with each other through the interiorthereof; and a sleeve means mounted in said housing extending into saidtank port and constituting an extension of such bore from the ad-'jacent service port, said sleeve 'means being operative tobloick one ofsaid openings as said valve spool is moved to one of said operatingpositions, saidsleeve means also being of smaller diameter than saidtank port to. thus definean annular passage through which fluid isadapted to flow. I v 10. The spool valve assembly of claim 9 whereinsaid housing is formed with another bore, and a relief valvecommunicated selectively with said service ports to ac: tuate suchcylinder assembly in eit'ner'direction, and a I float position whereatsaid service ports are 1 communicated with each other and said 'inletand tank ports '{are' communicated with each other; and first and secondrestrictor means respectively eflective,in one operating position onlyof said spool, to build up a back pressure in one service port when thatservice port is communicated with said tank port and, in the floatposition of said spool, 1

bleed fluid from between said intercommunicating',service ports: to saidtank port andyto build up a back pressure which, in the case ofadifferential displacement cylinder.

in such another bore to communicatesaid inlet port with said tankport'when' the fluidpressure in said inlet port exceeds a predeterminedmaximum, such fluid flowing through said tank port and around saidsleeve means.

, 11'. Thespool valve assembly-of c1aim 9 wherein the inner end of saidsleeve means is spaced axially outwardly from the respective end of saidbore and the adjacent service port.

12. A'spool valve assemblycomprising a housing formed with a boreintersected, axially therealong by a pressure inlet port, a tank port,and aservice port adapted for connection with a hydraulic.cylinder'assembly to actuate the piston thereof; a valve spool axiallyrecipassembly, accommodates excess fiuid from one end and preventscavitation in the other end; said first restrictor. comprising aperforate sleeve mounted in said housing to constitute an'extension ofsuch bore and through which fluid flows from said one service port tosaid tank port.

4. The spool valve assembly of claim 3 wherein said second restrictorcomprises an orifice through the wall.

of said spool, said spool having openings leading to the interiorthereof which'communicate with the respective A service ports when saidspool is in the float position.

5. The spool valve assembly of claim4 wherein said spool is formed withopenings through the wall thereof which register with the respectiveservice ports in the float position.

6. The spool valve assembly bore is enlarged at both ends to receivesaid sleeves inter changeably therein.

7. The spool valve assembly of claim 6 wherein'sai'd spool has springmeans at one end effective to automatical- I Ely return it to neutralposition from both operating positions and an actuating portion at'theother end by which it may be manually shifted from neutral to saidoperating and, float positions, said spool, together with said sleeves,being.

reversible end for end in such bore to'thus reverse the with respect tosaid housing. 1 V

8. The spool, valve assembly of claim 7 wherein said housing is formedwith another bore which is parallel'to position of said spring meansand'said actuating portion such valve spool bore, and a relief valve insuch another bore to communicate said inlet port with said tank' port ofclaim 5 wherein such,

rocable in such bore and formed with alternate lands and grooves toprovide a neutral positionwhereat said inlet port and tank port are influid communication and said service port is blocked by a land of saidspool, two operating positions whereat said "inlet portand tank port arecommunicated selectively with said service port; and restrictor meanseffective to build u'pa back pressure in said service-portwhencommunicated with said tank port; said restrictor means comprising aperforate sleeve mounted in said housing to constitute an extension ofsuch bore and through which fluid flows from said service port to saidtank port.

13. A' spool valve assembly comprising a housing "formed with 'a boreintersected axially therealongiby a pressure inlet port, a tank port,and; a pair of service ports adapted for connection with a hydrauliccylinder assembly to raise and lower a load on the piston thereof;

a valve spool'axially reciproca ble in such bore and formed withalternate lands and grooves and with openings through certain landsthereof to provide a neutral position whereat said inlet port-andtankport are in fluid communication and said service ports are blocked bylands of said spool, and two operating positions whereat said I inletport and tank port are communicatedselectively when the fluid pressurein saidinlet port exceeds a predetermined maximum, said reliefvalve-having at one end thereof, adjusting means by which the openingpres-' sure is changed, such another bore and relief 'valve' beingformed so that said adjusting means may be-disposed adjacent either endof such another bore 9. A spool valve assembly comprising a housingformed with a bore intersected axially therealong by a pressure inletport, a tank port, and a pair of service ports adapted for connectionwith a h ydrauliccylinder assembly-tdraise and lower a load on thepistonthereof; a 'hollow valve spool axially reciprocable in such bore andformed with .vvithsaidservice ports to actuate such cylinder assembly ineither direction; and restrictor means eflective in. at;

least one operating position to build up a back pressure in one serviceport when that service'por-t is communicated with said tank port; saidrestrictor means comprising a perforate sleeve mounted in said housingto constitute an extensionof such'bore and through which fluid flowsfrom said one service port to said tank port.

1. A SPOOL VALVE ASSEMBLY COMPRISING A HOUSING FORMED WITH A BOREINTERSECTED AXIALLY THEREALONG BY A PRESSURE INLET PORT, A TANK PORT,AND A PAIR OF SERVICE PORTS ADAPTED FOR CONNECTION WITH A HYDRAULICCYLINDER ASSEMBLY TO RAISE AND LOWER A LOAD ON THE PISTON THEREOF; AHOLLOW VALVE SPOOL AXIALLY RECIPROCABLE IN SUCH BORE AND FORMED WITHALTERNATE LANDS AND GROOVES AND WITH OPENINGS THROUGH CERTAIN LANDSTHEREOF TO PROVIDE A NEUTRAL POSITION WHEREAT SAID INLET AND TANK PORTSARE IN FLUID COMMUNICATION AND SAID SERVICE PORTS ARE BLOCKED BY LANDSOF SAID SPOOL, TWO OPERATING POSITIONS WHEREAT SAID INLET AND TANK PORTSARE COMMUNICATED SELECTIVELY WITH SAID SERVICE PORTS TO ACTUATE SUCHCYLINDER ASSEMBLY IN EITHER DIRECTION; AND A FLOAT POSITION WHEREAT SAIDSERVICE PORTS ARE COMMUNICATED WITH EACH OTHER AND SAID INLET AND TANKPORTS ARE COMMUNICATED WITH EACH OTHER; AND RESTRICTOR MEANS EFFECTIVE,IN ONE OPERATING POSITION ONLY, TO BUILD UP A BACK PRESSURE IN ONESERVICE PORT WHEN THAT SERVICE PORT IS COMMUNICATED WITH SAID TANK PORT;SAID RESTRICTOR MEANS COMPRISING A PERFORATE SLEEVE MOUNTED IN SAIDHOUSING TO CONSTITUTE AN EXTENSION OF SUCH BORE AND THROUGH WHICH FLUIDFLOWS FROM SAID ONE SERVICE PORT TO SAID TANK PORT.